A requisite for the organizational complexity of eucaryotic cells is the efficient delivery of polypeptides from their sites of synthesis to the eventual sites of their function. The research this proposal addresses is a heretofore unexamined component of this problem, the mechanism by which a subclass of peripheral cell-surface glycoproteins are localized to the external surface of a cells' plasma membrane. We have recently completed two studies, the first of which determined that in embryonic chick neural retina glycoproteins that were recognized by the cell-surface protein ligatin contained high mannose-type oligosaccharides terminating in phosphodiester-linked glucose residues. The second described the presence of a phosphoglucosyltransferase responsible for the addition of those terminal residues. The hypothesis we propose to investigate suggests that this phosphoglucosyltransferase plays a salient role in the coding of its acceptor proteins for their subsequent transport to the cell surface. The proteins then remain at the cell surface through association with ligatin. We propose to address the following specific aims: 1) to identify the endogenous acceptor proteins of the phosphoglucosyltransferase in embryonic chick neural retina. We will compare polyacrylamide gels of the endogenous acceptor proteins with gels obtained from metabolically 32p-labelled cell-surface proteins associated with ligatin. We will also determine the ability of endogenous acceptor proteins to bind to ligatin affinity columns; 2) To purify and characterize the phosphoglucosyltransferase. In particular we plan to determine if glycoproteins destined for the cell surface are preferentially recognized by the transferase, and if so, to determine if intact tertiary structure of the acceptors is necessary of optimal activity; 3) To examine intracellular membrane fractions for an intracellular receptor for phosphoglucosyl-terminating oligosaccharides. Such a receptor could be necessary for the transport of the acceptor proteins to the cell surface; 4) To localize using both subcellular fraction techniques and electron microscope autoradiography the intracellular localization of the phosphoglucosyltransferase and to determine the route its acceptor proteins take as they are transported to the cell surface.